Method and apparatus for cleaning foundry sand



F. 1 WARD 2,766,496

METHOD AND APPARATUS FOR CLEANING FouNDRY SAND Oct. 16, 1956 Filed Feb.2, 1952 INVENTOR. z'c

United States Patent O METHOD AND APPARATUS F R CLEANNG FOUNDRY SANDFrederic L. Ward, Pontiac, Mich., assigner, by messe assignments, toRobert W. Ward Company, Eetrot, Mich., a corporation of MichiganApplication February 2, 1952, Serial No. 269,621 4 Claims. (Cl. 22-89)This invention relates to a process and apparatus for cleaning sand :andmore particularly to a process and apparatus which is particularlyeffective for removing carbon adhered to particles of used foundry sandwhereby the sand is conditioned for Ireuse as a foundry or core sand.

In the usual practice for preparing foundry molds sand is mixed with anorganic binder and the resulting mass is formed to produce a mold havingthe desired shape. When the mold is contacted with molten metal theorganic binder tends to carbonize leaving a considerable amount ofcarbon or carbonaceous material deposited on the sand. This carbonprevents the sand from being used again for preparing a mold,particularly in those instances Where precision casting is required.Many thousands of tons of foundry sand are discarded each year becausethe presence of carbonaceous material and other materials renders thesand unsuitable for reuse.

Many methods have been proposed in the past for separating carbonaceousmaterial from foundry sand so that the sand may be reutilized, however,none of them have been economically practical. A particular object ofthis invention is the provision of a method and apparatus for cleaning aused foundry sand in such a manner that it may be readily reused.

A further object of this invention is the provision of a method andapparatus for efficiently cleaning foundry sand at a very low cost andwith a minimum of equipment.

A still further objectk of this invention is the provision of a methodand apparatus for cleaning used foundry sand whereby substantially allof the carbon and fines are removed so that the clean product may beutilized as a core sand if desired.

A still further object of this invention is the provision of :anapparatus for cleaning foundry sand which may be constructed fromreadily available equipment.

A still further object of this invention is the provision of a processfor cleaning foundry sand which isv more suitable for use in manyinstances than fresh sand for similar purposes.

Further and additional objects will appear from the followingdescription, the accompanying drawings and the appended claims.

In accordance with one embodiment of this invention, aA process andapparatus have b een provided which dislodges carbon from sand particlesby hurling two streams of sand in liquid suspension against each other`at high velocity. The process contemplates moving two streams of sandin liquid suspension at high velocity in opposite directions andimpinging these ystreams one against the other ywhereby the carbon andother foreign material adhering to the sand particles are dislodged. Inaccordance with a preferred embodiment of this invention, theprocess isone which is cyclic in nature wherein the liquid suspension of impingedsand particles, is divided ICC into two streams and recycled to the twohigh velocity streams for reimpingement. The process of this inventionmay be conducted as a batch operation or it may be. made continuous ifdesired.

Preferably the Aapparatus in which the process of this invention iscarried out comprises a cylindrical scrubber having av horizontallydisposed axis. The scrubber comprises a central abrasion or impingementzone and two oppositely disposed end zones. Means including a conduitare providedl for circulating the impinged streams from the impingementor abrasion zone back to the two end zones exteriorly of the scrubber.The sand suspension thathas been cycled throughl the scrubber may thenbe passed to one or more flotation zones in order to seperate thedislodgedl carbon and nes from the scrubbed sand particles. Preferablyhydraulic jets having relatively long venturi throats are employed fortransporting the sand-water suspension from the scrubbing zone to theflotationzones. The jets are particularly useful since they provideadditional means for scrubbing the sand particles as they pass. throughthe equipment.

In accordance withI one embodiment of this invention, a battery ofscrubbing zones may be employed with flotation means interposed betweensuccessive scrubbing zones whereby carbon and fines are removed from thescrubbed suspension prior to the introduction of the suspension of sandinto the next succeeding scrubbing zone. After the scrubbed sand haspassed through the final scrubber and flotation zone, it may then bepassed through a hydraulic separator or classifier in order to removelast traces of soluble matter, fines, carbon. or other oversize orlightweight particles.

For a more complete understanding of this invention, reference will. nowbe made to the accompanying drawing which is a more or less diagrammaticshowing of one form of apparatus in which the process. of this inventionmay be carried out.

The apparatus shown in the drawing comprises a hopper or bin 10 whichserves as temporary storage means for used foundry sand. In operationthe dry sand is discharged through valve 12 into a grinder or pulverizer14 wherein the lumps of foundry sand are comminuted to reduce them toindividual sand particle size. The dry material is then dischargedthrough spout 16 onto a 30 mesh vibrating screen 18. Oversize particlesare collected in a receptacle 20 for discard. Water is sprayed onto theupper surface of the vibrating screen 18 through a plurality of spraynozzles 2-2 and the water and sand including the fines pass through thescreen 18 into a hopper 24. The sand is maintained in a, fluidizedaqueous suspension by continuously introducing a small amount of waterinto the bottom of the hopper 24 through a valved 4conduit 26.

A uid suspensionl of` sand and water is withdrawn from the bottom of thehopper 24 througha hydraulic jet 28, and forced through a conduit 30into the top of a flotation chamber 32. The jet 28 is a high pressurepump operated by a stream of water discharged at about 800 p. s. i.through thenozzle 34 into the jet chamber 36 as will be readilyunderstood. Preferably theV venturi throat 38 of the jet isv long landnarrow in construction in order that a large amount of turbulence willbe imparted to the jetted sand suspension.l This turbulence results inthe abrasion of the sand particles which serves in some degree to scruboff some of the carbon that may be adhering thereto.

The jetted mixture is discharged into the flotation chamber 32 andlightweight carbon particles or lines contained in the suspension may befloated off of the top by excess water supplied by the jet through anoverflow means 40. A small amount of water is continuously introducedinto the bottom of the otation chamber 32 by means of a valved conduit42 in order to prevent sand from packing in the bottom of the chamber 32and to provide in part excess water for otation out of the overflow 40as above described. A suspension of sand and water is continuously orintermittently withdrawn from the chamber 32 through a valved tting 44and introduced into a chamber 46 from which additional lightweightcarbon particles and finesV may be separated from the sand by aflotation method, the latter being withdrawn through the overflow spout48. The fluid suspension including sand particles having carbon adheredthereto is then continuously or intermittently withdrawn from theflotation chamber 46through the valved conduit 50 for discharge into aiirst scrubbing7 zone. Water may be continuously introduced into theconduit 50 through valved lines 51 and 53 in order to prevent packing ofsand within the conduit 50 and adjacent the valve.

The sand suspension is discharged from the conduit 50 into a funnel 52which forms a part of a first scrubbing zone 54. This zone comprises ahorizontally disposed cylindrical chamber or scrubber 56 defining acentrally located impingement or abrasion zone 58 and oppositelydisposed end zones 60 and 62. Extending through the chamber 56 is anaxial shaft 64 having a plurality of propellers or impellers 66, 68, 70and 72 rigidly aixed thereto. The propellers may be provided with anabrasion-resistant coating of rubber or other material if desired.Propellers 66 and 68 are pitched in one direction and Propellers 70 and72 are pitched in the opposite direction so that when the shaft 64 isrotated at a high rate of speed by any convenient means (not shown) thePropellers will hurl a fiuid sand suspension from the ends 60 and 62 ofthe chamber toward the central irnpingement zone 58 at a high velocity.The shaft 64 is bearinged in the opposing end walls of the chamber 58 bysuitable water bearings 74 into which water under pressure is appliedthrough conduits 76 thereby providing a continuous flow of water intothe scrubber 56 and preventing sand from nding its way into thesebearings 74. These bearings of course are shown only diagrammatically inthe drawing.

The scrubbing chamber 56 is provided with a bottom discharge valve 78which may be utilized for cleaning operations or for discharging thescrubbed suspension from the scrubbing zone when it is desired tooperate the scrubber batchwise. Extending upwardly from the impingementzone 58 of the scrubber 56 is a standpipe 80 communicating at its upperend with a pair of stream dividing conduitsV 32 and 84. Conduit 82discharges into the funnel 52 and conduit 84 similarly discharges into asimilar funnel 86. The funnels 52 and 86 discharge into opposite ends ofthe scrubbing chamber 56, it being noted that the discharge end of eachof these funnels terminates at a point closely adjacent the shaft 64 andbetween a pair of impellers 66 and 68 and 70 and 72 which serve to hurlthe sand-water suspension from the end zones 60 and 62 toward each otherto the zone of impingement 58. 1t has been found preferable in thismodification to have the discharge ends of the tunnels 52 and 86terminate closely adjacent the shaft 64 since by this construction ithas been found possible fully to till the scrubber S6 with a suspensionof sand in water during operation. Also the provision of the standpipeextending vertically above the impingement zone for a substantialdistance permits the maintenance of a pressure in the impingement zonewhich in combination with the discharge ends of the funnels 52 and 86prevents the formation of undesired air pockets within the scrubbingchamber during operation.

Thus when a suspension of sand in water is passed into the funnel 52 andthe scrubbing chamber 56 and after the scrubber has become substantiallyfull of the uid suspension then the rapid rotation of the shaft 64 byany suitable means causes the formation of two streams of sand and watersuspension moving in opposite directions to the impingement zone 58. Atthis point the sand particles are rapidly hurled against each otherwhereby the sand particles strike against each other and the carbon isdislodged. The impinged stream is withdrawn from the scrubber throughthe standpipe 80 and is divided by the conduits 82 and 84 and falls backinto the tunnels 52 and 86 whereafter it is recycled to the scrubber 56in a manner that will be understood. Thus means are provided exteriorlyof the chamber 56 for recirculating the suspension from the impingementzone to the respective end zones.

It is important to note that the shaft 64 is rotated at a high rate inorder to permit the oppositely moving streams of suspension to be hurledagainst each other at high velocity. Thus it is preferred that theperipheral speed of outer ends of the impellers 66, 68, 70 and 72 bebetween 3,000 and 5,000 feet per minute in order to impart the desiredvelocity to the impinging streams. The velocity is such that the heatgenerated on account of the impingement and abrasion is suiiicient toraise the temperature of the sand and water suspension to a value aboveabout 120 F. after about ten minutes of operation. This temperatureincrease further functions to dislodge carbon by reason of thermalexpansion etects.

After the sand is subjected to a desired degree of abrasion or scrubbingin the scrubbing zone 54, then it may be withdrawn through the valve 78for further treatment. However, it is preferred that the scrubbed sandbe continuously or intermittently withdrawn from the apparatus throughvalved conduits 88 and 90 extending from an upper end of the standpipe80. It will be noted that withdrawal conduits 88 and 90 are locatedupstream of the discharge end of conduit 50 so that in a continuousoperation all sand will pass at least once through the scrubber chamberand impingement zone. The conduits 88 and 90 merge into a conduit 92which supplies the intiuent for a jet pump 94 which serves to elevatethe scrubbed sand-water mixture through conduit 96 to a flotation zone98. The jet pump 94 has substantially the same structure as jet pump 28previously described and is operated with a stream of water at about 800p. s. i. scrubbed-off particles of carbon, as well as nes, are floatedoif through the overow spout 100 and the sand suspension is passedthrough a valved conduit 102 and branch conduits 104 and 106 to a secondscrubbing zone 10S.

Scrubbing zone 103 is similar to scrubbing zone 54 in that it comprisesa cylindrical scrubbing chamber having a rotatable shaft 112 extendingtherethrough. The shaft has fixedly mounted thereon propellers 114, 116,118 and 120 which are pitched in such a manner as t0 force a suspensionof sand and water toward the central area 122 of the scrubbing chamber.In operation the shaft 112 also rotates at a sufficient speed to movestreams of sand and water suspension at high velocities in oppositedirection to the zone of impingement 122 wherein the carbon is dislodgedfrom the particles of sand. The mixture is then forced by the pressuresobtaining in the impingement zone 122 through an upwardly extendingstandpipe 124 from which it is passed to a pair of legs 126 and 128 forreintroduction into the end zones of the scrubbing chamber 110. Thus thesand particles in the scrubbing zone 108 are subjected to a plurality ofimpingements and the travel of material through this zone (as well asthrough the zone 54) is in the shape of a pair of rings which rings areconcentric throughout a portion of their length, the concentric portionbeing in this instance the standpipe 124. If desired, the scrubbed sandmay be withdrawn from the chamber 110 through 'a valved conduit 130.Preferably, however, it is withdrawn from the standpipe 124 through apair of valved conduits 132 and pumped by another jet pump 134 toanother flotation chamber 136' from which additional carbonV and finesare floated from the suspension. Thereafter the sand suspension isvpassed through another scrubbing zone 138 which may be substantiallythe same as the scrubbing zone 108 and the sand isscrubbed in the samemanner.

In scrubbing zones 108 and 138 sand and water are circulated as abovedescribed in two closed rings. The entire system at this point is closedso that no air is introduced into the scrubbing chambers. In scrubbingzone 54, air is prevented from entering the scrubbing chamber by alwaysmaintaining a substantial level of suspension in each of the openfunnels 52 and 86.

The sand scrubbed in zone 138 is eventually passed to a flotationchamber 140, then through a jet pump 142, another flotation chamber 144and introduced into a hydraulic classifier. This classifier comprises amain chamber 146 having a tube 148 extending downwardly therein andthrough which the sand suspension descends after being discharged fromthe flotation chamber 144. The chamber 146 is filled with water andmeans are provided for flowing water in a stream upwardly through thetube 148 at a constant rate. The sand particles settle in the water inthe tube but the upward movement of the water carries off the morebuoyant particles for overflow into an upper annular chamber 150 andultimate discharge through a conduit 152. The supply of water to theclassier 146 is maintained constant by means of a flow regulator 154.This regulator includes a chamber 156 into which water is continuouslyintroduced through conduit 158. Water is withdrawn from the chamber 156through a plurality of conduits 160 and 162 for introduction at spacedpoints into the annular chamber 164 between the tube 148 and the insidewalls of the chamber 146. Only two conduits 160 and 162 are shown in thedrawing, but it is preferred that there be four of them having fourdischarge ends spaced equally around the chamber 164. The rate of flowof water into the chamber 156 through the tube 158 is somewhat greaterthan that which can be accommodated by the conduits 160 and 162discharging into the classifier chamber 146. Thus a portion of the waterintroduced into the chamber 156 is withdrawn by a vertically adjustableoverflow conduit 166. It will be apparent that the vertical adjustmentof the conduit 166 determines the pressure head on the water passed tothe hydraulic classifier through the conduits 160 and 162. Obviouslythis pressure head determines the rate of flow of the water downwardlythrough the annular passageway 164 and upwardly through the tube 148.Therefore the height of the overflow tube 166 is important indetermining the particle' size of sand that will settle into the bottomof the classifier 146. It will be apparent from the drawing that annularring 167 separates the inflow chamber 164 from the overow chamber 150.

The cleaned sand having a uniform particle size collects in the bottomof the classifier and the level therein may be observed by a sight glass168. The sand may be withdrawn therefrom as required through a valveconduit 170 whereafter it is dried in the usual fashion and may bereused as a foundry or core sand.

It will be apparent from the foregoing description that an efficientprocess and apparatus has been developed for cleaning used foundry sandvery eciently and at a relatively high rate. The apparatus may be usedintermittently or continuously as desired. For small operations only onescrubber is necessary, care being taken to circulate the sand throughthe scrubbing system for a sufficient time to dislodge substantially allof the carbon from the sand particles. However, in large operations itis preferred to employ a battery of two, three or more scrubbers asindicated in the drawing.

In the operation of the apparatus it has been found that sand may besatisfactorily cleaned where the average total residence time of thesand particles in the several scrubbing zones is from ten minutes to onehour. The sand-water suspension in each scrubbing chamber has a highpercentage of sand, suitable ratios being between about 20 and 100gallons ofr water for each ton of dry sand, an important considerationbeing tofprovide a fluid stream having a high concentration of particlesto ensure their mutual bombardment when the two streams are impingedagainst each other. If desired, suitable detergents or acid or alkalinewashing agents, such as sodium acid fluoride or sodium hydroxide may beadded to the suspension being scrubbed in order to assist in the removalof carbon from the particles. These agents are removed from the finalsand particles in the flotation and hydraulic classication operations.In a system in which the individual scrubbing chambers have a diameterof 20 inches and are about 46 inches in length, in which the centerstandpipe is about 7 feet high and 6 inches in diameter, and in whichthe propellers are about 17 inches in diameter and rotate at a rate ofabout 850 revolutions per minute, the sand will be adequately cleanedwhen the total average residence time of the particles in the severalscrubbing zones is between about 10 minutes and about one hour.

While particular embodiments of this invention are suggested above, itwill be understood, of course, that the invention is not to be limitedthereto, since many modifications may be made, and it is contemplated,therefore, by the appended claims, to cover any such modifications asfall within the true spirit and scope of this invention.

I claim:

l. Process of cleaning used foundry sand which comprises the steps ofscreening the sand in presence of water to remove oversized adventitiousmaterial, fluidizing the sand with a jet of water and passing it torelatively quiescent settling zones wherein loose carbonaceousimpurities will be floated off, transferring the residual sand to afirst attrition chamber in which said sand while fiuidized with water issubjected to attrition by impelling means hurling the sand particlesagainst each other, transferring the thus treated sand to a furthersettling zone wherein carbonaceous particles which have been loosenedfrom the sand are fioated off; a-gain submitting the sand in iluidizedcondition to attrition in the manner hereinabove recited, and againpassing the treated sand through a settling zone.

2. The process as recited in claim l, in which the sand is treated athird time in an attrition chamber.

3. T he process as recited in claim 2 in which a final elutriation stepfollows the operations to remove clay-like impurities smaller than thegrains of the sand.

4. Apparatus for cleaning used foundry sand which comprises means forscreening the sand in the presence of water to remove over-sizedadventitious material therefrom, jet means for fiuidizing the residualsand, and means for passing it to a quiescent settling zone, a settlingzone provided with means for floating off loose carbonaceous impurities,an attrition chamber comprising a housing having an elongated horizontalaxis, a shaft passing therethrough, means for transferring the residualsand to said attrition chamber, propellers on said shaft arranged so asto throw liquid in opposed directions toward the center of said chamber,exit means on said chamber for discharging the material therefrom, andmeans for introducing portions of the material thus discharged to saidchamber, means connected with said discharge means for transferringtreated sand and water in fiuidized condition to a second quiescentsettling zone, and means for passing sand settled in said second zone toa second attrition chamber, which mechanically is substantiallyidentical to the first mentioned attrition chamber, a further quiescentsettling zone, and means for passing settled-out sand therein to anelutriation zone, means for passing water into the bottom of said zoneto wash from the sand therein particles lighter than the sand particles,and means for finally discharging sand from said elutriation zone.

(References on following page) UNITED STATES PATENTS Luckenbach Feb. 22,1881 Conkling July 3, 1888 5 Podszus Feb. 16, 1926 Runyan Oct. 23, 1928Wiegand Jan. 1, 1946 Connolly Aug. 9, 1949 Luce et a1. Aug. 30, 1949Tomek et a1 Jan. 16, 1951 FOREIGN PATENTS Germany July 17, 1926 GermanyJuly 17, 1926

